Recent advances in epitaxial transfer and vapor-liquid-solid growth (VLS) have demonstrated precise materials integration in semiconductor nanostructures. These nanostructures will likely play a key role in the future of electronic and photonic devices. Advantages of multi-material nanostructures range from strain induced gain in charge carrier mobility to composition dependent band gap engineering. Epitaxial transfer produces high performance electronic and photonic devices. However, epitaxial transfer still involves traditional semiconductor fabrication, which may not be the best option when performance is not the only design driver. Amongst these, solid-state semiconductor photovoltaic applications would greatly benefit from a less demanding materials integration alternative. VLS growth offers a cost-effective wide library of available materials ranging from Si, Ge, Si1-xGex and III-Vs. While geometry and placement control has been greatly improved, obtaining deterministic growth for effective on-chip integration is still challenging.
An intriguing strategy is to localize growth using scanning probes instead of a catalyst particle. This strategy allows precise control over growth placement as well as growth direction. In this fashion, metallic and semiconductor features have been demonstrated via scanning tunneling microscope chemical vapor deposition (STM-CVD). However, low throughput and high vacuum conditions required during growth limit such nanostructures to laboratory devices. The atomic force microscope (AFM) can fabricate nanostructures in ambient conditions. Several AFM techniques such as dip-pen nanolithography (DPN) and high-field carbon direct-write have been successfully demonstrated with greatly increased throughput. DPN affords fast writing at large scale with multiple self-aligned parallel tips. High throughput large-scale carbon direct-write can be performed at 1 cm s−1 tip speeds or by using microstructured conducting stamps that mimic multiple parallel tips.
In spite of recent advances in methods for forming nanostructures, further developments related to parallel fabrication methods for inorganic nanostructures are still desirable.